A Distributed Antenna System (DAS) typically includes one or more master units that are communicatively coupled with a plurality of remote antenna units, where each remote antenna unit can be coupled directly to one or more of the master units or indirectly via one or more other remote antenna units and/or via one or more intermediary or expansion units. A DAS is typically used to improve the coverage provided by one or more base stations that are coupled to the master units. These base stations can be coupled to the master units via one or more cables or via a wireless connection, for example, using one or more donor antennas. The wireless service provided by the base stations can included commercial cellular service and/or private or public safety wireless communications.
In such a safety application, the safety wireless capacity provided by the DAS and the associated base-station-related equipment during normal operations may not be sufficient in emergency situations (such as a fire or security event) due to the presence of many additional users of the safety wireless service. As a result, it is common to provision a DAS used for such safety applications with additional base-station-related and DAS equipment (base stations, repeaters, etc.) that operate in a standby mode during normal operations but can be activated in emergency situations in order to provide increased safety wireless service capacity when necessary.
When planning for coverage within public safety relevant facilities by emergency services providers, the signal distributing infrastructure of the DAS may be shared between private and public safety services, each operating on their own frequency bands. For example the assigned licensed bands for the German Public Safety Digital Radio (BDBOS) TETRA network in Germany are 380-385 MHz for uplink communications and 390-395 MHz in downlink communications. For private safety services, different bands are used. For example, 415-420 MHz may be used for uplink communications and 425-430 MHz may be used for downlink communications for private safety services. Public safety signals are usually used by government agencies, such as police or fire, and public safety coverage is available from base stations provided across large geographic regions (for example, nationwide coverage). Private safety signal coverage, in contrast, is usually found within specific facilities or other areas of private service responsibility, for example, for the use of facility operator.
Subways, and specifically subway tubes, are one example of a facility where the communication infrastructure for both public and private safety services are extended and distributed. It is understood that subway trains may operate on tracks in tunnels below ground, and also on tracks above ground. However, while coverage for private safety services may be desired throughout the subway facility, distributing public safety communications coverage to above ground segments may cause interference with public safety communications coverage provided by other base stations operating in that area. As such, it may be required by regulations that public safety communications coverage by the subway operator's DAS should extend only to the below ground segments of the subway system to avoid interference with the signals from local public safety communications base stations operating close to the above ground segments.
It is therefore highly desirable for remote antenna units operating in above ground segments to be able to switch “off” the public safety band. It is also desirable to be able to selectively switch “on” the public safety band for those same remote antenna units for some emergency cases where the local base station that normally provides coverage around an above ground segment of a subway tube fails and cannot provide public safety coverage in that area.
One standard solution to this problem is for each remote unit to have separately operated communication paths in each remote antenna unit for each band—one for public safety coverage and one for private safety coverage. Then, the power amplifier, low noise amplifier, and/or other electronics for uplink and downlink transport of the public safety communications band may be switched off for those remote units operating in above ground segments. This solution has a big disadvantage however in terms of price since two expensive power amplifier modules (in addition to other RF components) would be needed, one for each downlink safety band of the remote unit. For public safety operators, this redundant and expensive equipment remains dormant most of the time, except for when emergency situations require its operation.